JPH0668433A - Magnetic tape containing abrasive material - Google Patents

Abstract

PURPOSE: To obtain a magnetic tape containing an abrasive which does not cause excess abrasion of a video head but decrease the peaks on the rough surface by grinding and moreover, which does not give bad effect on the magnetic and mechanical characteristics of the magnetic tape. CONSTITUTION: The magnetic tape consists of a nonmagnetic base layer and a magnetic layer formed on the base layer. The magnetic layer contains a magnetic hard pigment and a nonmagnetic pigment dispersed in a polymer binder. The magnetic tape has a function to polish and clean the contact part of a magnetic tape cassette and a recording/reproducing device in contact with the magnetic layer. The magnetic pigment consists of acicular CrO2 having at least 26m<2> /g BET value, and the nonmagnetic pigment has at least 9 Mohs' hardness and 0.1 to 2μm primary particle size and 1 to 130m<2> /g BET value. The magnetic layer has <0.02μm Ra.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-magnetic substrate layer, a magnetic hard pigment and a non-magnetic pigment having a particle size of less than 2 μm, and a polymer binder and optionally other additives.
For example, it has a dispersed magnetic layer applied on the above base layer containing a dispersant, a curing agent, a plasticizer, and a lubricant, and polishes and purifies a portion in contact with the magnetic layer in a magnetic tape cassette and recording / reproducing apparatus The present invention relates to a magnetic tape having the action of

When a magnetic recording medium, for example, a magnetic tape is used for a long period of time, abrasion occurs, and the powder thus produced is deposited on the surface of the magnetic head. The dust in the atmosphere also accumulates and pollutes the magnetic head. This type of deposit contributes to the degradation of audio and video quality, which in turn leads to level drops during recording and playback. Another cause of the level drop is so-called head deterioration. This can cause the essentially monocrystalline magnetic head surface to change to the polycrystalline state under the strain effect of the magnetic tape pulled over the magnetic head.

A general development objective in the manufacture of magnetic tapes is to minimize the content of non-magnetic material in the recording layer so as not to impair the magnetic properties.

Nevertheless, when magnetic iron oxides (generally cobalt-doped) are used as recording particles, in addition to the polymer binders necessary to bind the magnetic pigments and provide the mechanical running behavior of the magnetic tape. There are two reasons for using a non-magnetic pigment as described below.

First, in many cases the wear resistance of magnetic tapes can only be satisfied by the addition of non-magnetic pigments, and secondly, when magnetic tapes are used for video recording, ie magnetic recording, magnetic iron oxide. Mohs' hardness requires constant and minor polishing of ferrite video magnetic heads, but is insufficient to achieve this. By adding a hard abrasive to this magnetic layer composition, the minimum and uniform head polishing desired to provide good magnetic contact between the tape and the head can be achieved. The composition of this magnetic layer is, for example, US Pat. No. 3,630,910.
No. 4,379,800 and West German Patent No. 3910488.

In the case of using the magnetic pigment CrO ₂ , the opposite situation occurs. That is, due to the high Mohs hardness of this magnetic pigment, the head may be excessively polished by the pigment. To address this, relatively soft inorganic pigments such as ZnO
And / or coating organic pigments with organic materials (eg "Transactions, On, Magnetics" Vol.-Mag. 2).
3, No. 1, pp. 103-105, January 1987). Smoothing the surface of the magnetic tape by calendering also has a control effect that provides the desired minimum head polishing. From this point of view, the use of non-magnetic hard pigments is problematic when CrO ₂ is used.
West German Patent No. 2554146 discloses a magnetic head cleaning method for a video recorder having a video monitor, wherein Al ₂ O _{3 having} a Mohs hardness of 9 against magnetic pigment CrO _2.
Is added as a non-magnetic pigment. The video test image was recorded on the magnetic tape manufactured according to the above disclosure, the tape was loaded into the video recorder, and the reproduction cleaning operation was performed until the test image was properly reproduced. At this point, the recorder was immediately stopped and the test cassette was tested. I had to get out. It is clear that the above process is very critical and will scratch the video head if not done properly. The Ra value of this magnetic tape is 0.05 to 0.12 μm, which is a markedly rough surface for use as a video tape.

Further US Pat. Nos. 4,138,229 and 4
No. 397911 discloses a cleaning tape for magnetic recording heads which does not contain magnetic pigments but contains inorganic pigments of different hardness and particle size or a mixture of inorganic and organic polymer powders.

Regardless of this, it has been found that some polishing effect is preferred not only for video heads. That is, some polishing is also advantageous for magnetic tape, and especially for other components in the video cassette that come into contact with that magnetic layer. Such a member, for example, a tape guide member or a tape diverting member, damages the tape magnetic layer with which the rough surface peak portion (relative to the valley portion) or the peak portion (relative to the valley portion of the rough surface) is damaged, thereby reproducing. Between visible,
This is because it causes audible interference.

However, experimental results have shown that the rough surface peak portion of this problem cannot be eliminated by magnetic pigments. This is because the magnetic pigments used for signal storage are composed of extremely fine grain sizes to minimize signal interference and provide high recording density. This kind of fine magnetic pigment having a certain degree of hardness brings about a slight polishing effect on each member in the cassette that comes into contact with the magnetic layer, but the rough surface peak portion of the contact surface of each member becomes a problem. Can only be slightly smoothed after a very long running of the tape. Therefore, the videocassette tape is scratched along its entire length, which makes the tape unusable. This is because, as described above, this scratch caused in the longitudinal direction causes continuous and visible troublesome streaking on the screen depending on its depth.

As expected, the relatively hard CrO ₂ pigment was used to perform the light and laborious grinding more quickly than was the case with the relatively soft iron oxide particles. Despite the slow polishing process, it was not possible to avoid its longitudinal scratches during tape running in a video cassette. Therefore, the known pigment can be used only when the respective members to be brought into contact with the magnetic tape have been completely smoothed beforehand, but this makes the manufacturing cost of the video cassette expensive due to the careful smoothing treatment. .

Therefore, the technical problem in this field is to bring about the polishing of the peak portion of the rough surface of the video head without causing the polishing of the video head remarkably excessively, and to adversely affect the magnetic and mechanical properties of the magnetic tape. It is an object to provide a magnetic tape containing an abrasive.

[0012]

SUMMARY OF THE INVENTION The technical problems mentioned above, however, include a non-magnetic substrate layer and a magnetic layer applied on the substrate layer, which contains magnetic hard pigments and non-magnetic pigments dispersed in a polymer binder. A magnetic tape having a function of polishing and cleaning a portion of the magnetic tape cassette and a magnetic layer in a recording / reproducing apparatus, the magnetic pigment having a needle-like shape having a BET value of at least 26 m ² / g. CrO ₂ , said non-magnetic pigment having a Mohs hardness of at least 9, a primary particle size of 0.1 to 2 μm and a BET value of 1 to 130 m ² / g and a magnetic tape magnetic layer of 0.02 μm. It has been found by the present inventors that a magnetic tape characterized by having a lower Ra value can be solved. According to the present invention, all the peaks of the rough surface on the surface of the member which the magnetic tape contacts can be removed by polishing in a short time of tape running. Nevertheless, the additional polishing action on the smoothed contact surface (video head after removal of rough surface peak, tape turning guide pin) is
Compared to the slight polishing effect of O ₂ particles, it is a level that can be completely ignored. Therefore, the present invention, after the rough surface peak removal of the member that comes into contact with the tape, that is, smoothing is performed,
It can result in a self-control method in which the polishing process can be stopped naturally.

Therefore, as will be described in more detail below, the addition of a suitable non-magnetic pigment makes it possible to use a hard magnetic pigment of the CrO ₂ type. This means that in the case of fast thermal duplication of video programs, for example, in the case of cassettes using inexpensive members such as metal tape diverting pins with a significantly rough surface structure, good quality images without interference can be obtained. It is especially advantageous for both and for the cassette manufacturer.

Of course, when adding a non-magnetic pigment, it is important to take care that coarse particles are not mixed in the magnetic layer so that the video head is not scratched. Also, excessively fine non-magnetic pigments cannot be used so as not to interfere with the selective polishing process.

According to the magnetic tape of the present invention, audio and video magnetic tape recorders (3.81 mm, 1/4 inch, 8 mm, 1/2 inch, Bethacam, R-DAT, 1 inch, 2 inches) of markedly different standards are provided. Even if used, it can bring about an excellent cleaning effect without causing scratches.

[0016]

The dispersion layer, ie the magnetic layer, can be produced by methods known per se, preferably using CrO ₂ having a Mohs hardness of approximately 8. Its coercive force is 25
It is preferably higher than kA / m and the BET value is at least 26 m ² / g. Other hard magnetic pigments, such as needle-shaped iron carbide or iron nitride, or mixtures thereof with CrO ₂ can also be used. Such pigments are disclosed, for example, in West German Patent Nos. 3512270, 3634283 and 3
634487, European Patent 312032, 34
No. 0689, 227104. Inorganic, non-magnetic pigments having a Mohs hardness of at least 9 such as Al ₂ O ₃ or chrome green, Cr ₂ O ₃ ,
It can be used as a so-called hard abrasive. These pigments range from 0.1 to 2 μm, especially less than 1 μm.
Next granularity, 1 from 130m ² / g, in particular from 5 25 m ² /
It is desirable to have a BET surface of g. SiC, garnet or SiO ₂ particles may also be used in the present invention. Cubic aluminum oxide pigments having an average primary particle size of 0.3 μm are particularly suitable for the purposes of the invention. The accompanying drawing substitute photograph (Fig. 1) shows a state in which the non-magnetic pigment of cubic aluminum oxide is dispersed and embedded in the magnetic layer containing acicular chromium dioxide particles (20,000 magnification, scanning). electronic microscope).

The polymeric binder used may be any of the typical hard or soft binders used in magnetic tapes, or mixtures thereof. Vinyl chloride, vinyl acetate and vinyl alcohol copolymers, vinylidene chloride and acrylonitrile copolymers, polyvinyl acetals such as polyvinyl formal or cellulose derivatives such as nitrocellulose and phenoxy resins, epoxy resins, polyester polyurethanes, polyether polyurethanes , Polycarbonate polyurethane, etc. are examples.

As the binder solvent, those well known in the art, such as tetrahydrofuran, dioxane, dimethylformamide, cyclohexanone, methyl ethyl ketone, toluene, methyl isobutyl ketone and any mixture thereof are used.

Dispersion aids are many known surface-active compounds,
For example fatty acid amines or diamines, fatty acids or ammonium salts thereof, lecithin, ethoxylated fatty acid derivatives, optionally ethoxylated phosphoric acid esters of aliphatic or aromatic, sulfosuccinic acid esters, sorbitan esters, aliphatic and aromatic sulfonic acids. Alternatively, it is selected from sulfonate, aliphatic alcohol sulfate and the like.

Other additives, including plasticizers, lubricants, hardeners,
For example, diisocyanates, and curing accelerators of known type can also be used for forming the magnetic recording layer of the present invention.

Knife coating the magnetic dispersion layer composition,
It is preferable that the dry magnetic layer is applied by a method such as extrusion coating or cascade coating so that the thickness of the dried magnetic layer is 2 to 10 μm.

A sheet of polyester, polyolefin, cellulose derivative or polycarbonate is used as the non-magnetic substrate layer. After applying the above magnetic layer to this, it is dried by an arbitrary method and the surface is smoothed by calendering. This treatment is carried out by feeding the laminated dry substrate layer under pressure at a surface temperature of 70 to 105 ° C. between a roller pair, for example a heated metal roller and a plastic roller. The magnetic tape thus obtained is cut into a desired width and stored in a cassette as needed.

The present invention is illustrated more specifically by the following examples, in which all amounts used are given in parts by weight. The dispersion layer for the magnetic layer was made into a dispersion liquid in a tank equipped with a turbo mixer in an amount ratio shown in Table 1 in advance, and was ground in a stirring ball mill filled with ceramic grinding balls having a diameter of 1 to 1.5 mm. It It is then combined with a binder solution having the composition shown below. 3.5 parts of diisocyanate (Desmodur L, a Bayer product) and 0.1 part of iron acetylacetonate in 6 parts of tetrahydrofuran were added to the solution of the cross-linking agent, and the magnetic dispersion was extruded by an extrusion coating device. A dry layer thickness of 2. on a 15 μm thick substrate layer of polyethylene terephthalate.
It was layered so as to have a thickness of 5 μm, oriented in the magnetic field in the longitudinal direction in the layering direction, dried, and calendered.

Composition of Binder Solution Solvent Tetrahydrofuran 100 Cyclohexanone 16 Lubricant Stearic Acid 6 Butylstearate 9 Binder Polyester Urethane 15 Polyvinyl Chloride / Vinyl Acetate / Vinyl Alcohol Copolymer (VAGH) 4 0.7 μm average particle size Al ₂ O ₃ (Alcoa of Ludwigshafen, P10fei product of Chemie
nst) in Examples 1, 2, 4, 5, 6 and 8 with Al ₂ O ₃ particles having an average primary particle size of 0.3 μm (Baikowski, France Roannecy, GE6, product of Shimmy). And as a non-magnetic inorganic pigment in 7 and 7.

[0025]

[Table 1] To test the magnetic and mechanical properties, the resulting magnetic tape was cut into 1/2 inch (12.5 mm) wide,
A VHS cassette was used for 2 hours (tape length: 173 m).

Using this, the following tests were conducted.

(1) Measurement of storage data by the standard method for VHS tape, (2) Measurement of head wear degree after complete 50 times running in a cassette under steady climatic conditions, and (3)
Testing of magnetic tape behavior against inexpensive tape deflection pins.

This test was conducted as follows (see FIG. 2).

The magnetic tape (1) to be tested coming from the feed spool (1) is guided by guide rollers (3, 4) which come into contact with the surface of the magnetic layer, and the tape deflection pin (5) taken out from an inexpensive commercial cassette is attached to the magnetic tape. A certain amount of tension is imparted by running, and the tape is taken up on the take-up spool (6) (tape running speed 5 mm / sec). Using a stereomicroscope (7) oriented perpendicular to the tape magnetic layer surface between the deflection pin (5) and the roller (4), the defect disappears under the light rays tangential to the tape. The length of the tape up to was measured visually. A videocassette equipped with inexpensive tape diverting pins was used to run a side-by-side test on the recorded test signal, which measures the time until the television screen is no longer defective.

Table 2 Signal-to-noise ratio Until tape defect disappears Head wear tape running length dB dB _rel (m) (μm) Example 1 52.3 0.2 1.6 3.4 Example 2 52.2 0.1 0.9 3.8 Example 3 52.0 0.2 1.1 3.3 Example 4 51. 9-0.2 0.6 4.0 Example 5 53.0 0.9 0.9 1.2 4.4 Example 6 52.8 0.7 1.0 1.0 4.9 Example 7 52.6 0.6 1.2 4.3 Example 8 52.7 0.6 0.7 5.3 5.3 Proportional ratio 1 52.1 0> 173 3.4 Proportional ratio 2 53.0 0.9> 173 4.5 As can be seen from Table 2, in the case of Examples 1 to 8 of the present invention, the tape defect disappears with a short tape running length, but in the contrasts 1 and 2, the tape defect still remains after the full length running. It did not disappear. The correlation between scratches visually observed under the microscope and the interference observed on the television screen is in good agreement. From Table 2, 1 to 4
% Aluminum oxide does not cause deterioration in the luminance signal-to-noise ratio, and the head polishing rate is 100%.
Within the VHS specification of 0.5 to 6 μm per hour, but even with the use of inexpensive, therefore rough, tape deflection pins, the scratching interference of the magnetic layer with which they come into contact quickly disappears. To do.

The average surface roughness (Ra value) of the magnetic layer surface is in the range of 0.005 to 0.015 μm for both the magnetic tapes of Examples 1 to 8 and the commercially available ordinary magnetic video tapes of Comparative Examples 1 and 2. Met.

For the purposes of the present invention, it is preferred to add 0.5 to 10% by weight, especially 1 to 4% by weight, of hard non-magnetic pigment to the magnetic pigment.

[Brief description of drawings]

FIG. 1 is a photograph as a substitute for a drawing (2000 magnification, scanning electron microscope) showing a state in which a cubic aluminum oxide pigment as a non-magnetic hard pigment is dispersed and embedded in a magnetic layer containing acicular chromium dioxide particles according to the present invention. Is.

FIG. 2 is a magnetic tape containing an abrasive according to the present invention (Example 1)
8 to 8) and a similar magnetic tape commercially available (comparative ratios 1 and 2) are shown in the drawings.

[Simple explanation of symbols]

 1 Feeding Spool 2 Test Magnetic Tape 3 Guide Roller 4 Guide Roller 5 Tape Deflection Pin 6 Take-up Spool 7 Stereoscopic Microscope

[Procedure amendment]

[Submission date] August 4, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hans-Heinrich, Kredner, Federal Republic of Germany, 8021, Hohenschev Trarun, Steinberg, 7

Claims (3)

[Claims] 1. A magnetic tape cassette and a recording / recording device comprising a non-magnetic substrate layer and a magnetic layer provided on the substrate layer, the magnetic hard pigment and the non-magnetic pigment being dispersedly contained in a polymer binder. A magnetic tape having a function of polishing and cleaning a portion in contact with a magnetic layer in a reproducing device, wherein the magnetic pigment has at least 26 m ² / g.
Needle-like CrO ₂ having a BET value of, wherein the non-magnetic pigment has a Mohs hardness of at least 9 and a hardness of 0.1 to 2
has a primary particle size of μm and a BET value of 1 to 130 m ² / g, and the magnetic tape magnetic layer has an R smaller than 0.02 μm.
A magnetic tape having an a value. 2. The magnetic tape according to claim 1, wherein the non-magnetic pigment has a primary particle size of less than 1 μm and an amount of 0.5 to 10% by weight based on the magnetic pigment. A with a BET value of 5 m ² / g
A magnetic tape comprising l ₂ O ₃ or Cr ₂ O ₃ . 3. The magnetic tape according to claim 1, wherein the non-magnetic pigment is cubic Al ₂ O ₃ .